[awc] HTTP client uses chunked transfer-encoding on H2

[ArtBlnd]

Expected Behavior

chunked transfer-encoding on H2 is removed. it should never appear

Current Behavior

when sending request, awc is inserting chunked transfer-encoding header if content-length does not exists.

Possible Solution

remove chunked transfer-encoding on H2 implementation.

Steps to Reproduce (for bugs)

set version on request builder as Version::HTTP_2

Context

Your Environment

• Rust Version (I.e, output of rustc -V): rustc 1.53.0 (53cb7b09b 2021-06-17)
• Actix Web Version: 3.0.0-beta.7